Gracefully degrade to getopt if getopt_long does not exist.

diff --git a/configure.ac b/configure.ac
index e9135cc..f446767 100644
--- a/configure.ac
+++ b/configure.ac
@@ -932,6 +932,7 @@
 	ftruncate64 \
 	getnetbyaddr \
 	getnetbyname \
+	getopt_long \
 	getpagesize \
 	getprotobyname \
 	getprotobynumber \
@@ -980,6 +981,7 @@
 	direct.h \
 	elf.h \
 	float.h \
+	getopt.h \
 	ieeefp.h \
 	io.h \
 	libio.h \